DSM-V: Criteria A
A. Disruption of identity characterized by two or more distinct personality states, which may be described in some cultures as an experience of possession. The disruption of marked discontinuity in sense of self and sense of agency, accompanied by related alterations in affect, behavior, consciousness, memory, perception, cognition, and/or sensory-motor functioning. These signs and symptoms may be observed by others or reported by the individual.
This is the primary criteria of being classified DID, and can be broken out into several required sub-criteria.
First let's define psychology terminology and psychology-think first, so that the meanings aren't hidden within the semantics:
Personality states: the DSM is not interested in diagnosis of people based on their subjective experience. It has to be objective, observable, criteria. So this is purely observational and clinical in terms of determining a diagnosis. What does the doctor see when you switch? A change in your "personality state" -- observable mannerisms and habits.
However, our "identity" -- as in Dissociative IDENTITY Disorder -- is nearly entirely subjective and self-reported. That leaves this criteria with some difficult and complicated ground to cover to bridge "observable" to "subjective" and not do so in anything related to layman's terms.
Marked: (pronounced MARK-ed) notable, repetitive. Something that stands out. This kinda lets the doctor off the hook if they don't notice, but also eliminates this criteria for a single or less significant instance of the defined criteria occurring.
Discontinuity in sense of self: this is a clinical observation of your subjective observations. How's that for an oxymoron? Even if you relate an experience as not feeling like yourself one day, that could ding this criteria (but note, no one criteria in this grouping is enough to tag you as DID). This criteria can be checked off by an alter who talks about you in the 3rd person, it could be an alter who asserts that they're not you. Any observation leaving your lips about you acting out of your own character or feeling significantly 'different' than yourself for any period of time.
Discontinuity in sense of agency: This is the practitioner's observation of self-reported irregularities in your own personal sense of control over yourself. If you describe yourself as having trouble doing things, self-direction, changes in ability, changes in your sense of self-control, then you could ping this criteria. This is a clinical observation of a subjective state — i.e. "the client's sense of agency". If you ever describe yourself like you feel like a passenger in your body while your body does things, if you are "watching your hands do things" or if you have said things you entirely did not mean or expect to say, this could fall under a loss of your sense of agency.
Related alterations in affect: Loss of sense of self & sense of agency alone would fall under "depersonalization" and is a separate dissociative disorder. Here's where we start to move more into separate "persons" or "identity" criteria. Affect (aah-FECT) is observed emotional states. How does someone look when they are sad and crying versus happy and crying? That is their affect. Another person may look entirely different when they are crying regardless of reason. Each person displays different expressions when in different emotional states. It's the observable presentation of emotional states. Having related alterations of affect means that the doctor can observe changes in emotional state related to the changes in sense of self or sense of agency. It's the beginning of an observable difference between how you feel versus who you are. Affect is all the unconscious communication such as "the look in your eyes" or a quivering lip, or pouting, or eyebrow movements, "real" versus "fake" smiles, etc. — subtle body language.
Alterations in behavior: observable changes in habitual movements, vocal changes, word choices, restlessness, hand-gesturing, gross body language (involving range of motion, leaning forward, repetitive movements, crossing arms or legs) etc.
Alterations in consciousness: Switching can sometimes change your level of connection to the present. One can change states and become sleepy, dreamy, highly alert, or behave on a higher level of consciousness, or turn into a spiritual "deep thinker", etc.
Alterations in memory: This is also hit on in Criteria B New: poorer recall, total recall of things normally forgotten, or highly compartmentalized recall, stuck in the past and no knowledge of how much time has passed, etc. Sometimes this can be remembering the same event from a different perspective as well.
Alterations in perception: If your stance on how you interpret the meaning of things changes, that hits this criteria. You may view things on a processing/subjective basis differently from others in the system. For example, one's opinion may be that mom is great, another's opinion may be that mom is abusive. Seeing things from different directions. Devil's advocate, changes in spiritual or religious belief, etc.
Alterations in cognition: Each involved party may have different levels of ability to think things through, process information, knowledge-base differences, emotional quotient, creativity, logical thinking, strategic planning, executive functioning, etc.
Alterations in sensory-motor functioning: this is a fun criteria. Each person/alter/resident may walk differently, or have a different posture, but most easily observed is differences in what is usually muscle-memory related unconscious functions (for adults anyway) such as handwriting. They may actually have different facial muscle tension which can significantly change some more malleable facial features. Some may have different sensory functions such as blindness, deafness, numbness, etc.
These signs and symptoms may be observed by others or reported by the individual': The doctor does not need to see this to diagnose DID: it can be observed by other clinicians or nurse-practitioners, etc. and the doctor can declare the diagnosis based on the observations of others. This probably also helps in diagnosing children who are heading towards a DID diagnosis. You can also tell a doctor about what you've observed, then receive a diagnosis as soon as they are certain that you had perceived fits with all of these sub-criteria and meets the other criteria.
Putting it Together
So in total: being diagnosed as DID requires 2 or more personality states — the person who walked into the office and one other.
The remainder of the criteria describes what they mean by "personality states" which is a good definition of "Identity" (or person) and since it can be self-reported "observation" here's a rephrasing in more plain English:
The existence of 2 or more (observable or reported) identities or people sharing a body, where these 2 identities are defined as having a distinct sense of "self" and "self-control" separate from each other, including different feelings, behavior, consciousness, memory, perception, intellect, senses, and/or abilities.
Note the criteria does not bullet point nor require a set number of sub-criteria to qualify. This is probably deliberate, which means that anything from fragments to full blow separate people sharing the same body can qualify.
This information is not presented as a means of self-diagnosis, but to attempt to explain the criteria to persons already diagnosed who may be confused about how the criteria apply to themselves.